What’s the difference between a “raw” and a “cooked” device driver?
The terms raw and cooked only apply to terminal drivers. "Cooked" is called canonical and "raw" is called non-canonical mode.
The terminal driver is, by default a line-based system: characters are buffered internally until a carriage return (Enter or Return) before it is passed to the program - this is called "cooked". This allows certain characters to be processed (see stty(1)), such as CtrlD, CtrlS, CtrlU, Backspace); essentially rudimentary line-editing. The terminal driver "cooks" the characters before serving them up.
The terminal can be placed into "raw" mode where the characters are not processed by the terminal driver, but are sent straight through (it can be set that INTR and QUIT characters are still processed). This allows programs like emacs and vi to use the entire screen more easily.
You can read more about this in the "Canonical mode" section of the termios(3) manpage.
The terms get used to describe terminal and disk I/O, but mean different things in each context.
Raw and cooked modes on a terminal device cover processing (character-at-a-time vs. line-at-a-time, there are also a few other differences).
A 'raw' disk device (/dev/rdsk/*) is a character device, and the /dev/dsk/ is a block device. IIRC the main difference is that the block device has kernel buffering, and fine grained control over I/O modes such as direct/mapped I/O can be specified on a raw defice.
A description of raw and cooked tty modes can be found here. A posting about raw vs cooked disk devices can be found here.